X-ray tube



Patented May 28, 1929.

UNITED STATES PATENT. OFFICE.

CLAYTON 'IBIDLE ULREY, OF EAST ORANGE, AND HARRY DE FORES,T MADDEN, 0F

NEWARK, NEW JERSEY, ASSIGNORS TO WESTINGHOUSE LAMP COMPANY, A. COR- PORATION OF PENNSYLVANIA.

I Z-BAY Tenn.

Application filed October 20, 1924. Seriat No. 744,549.

is that the tube shall operate substantially free from gaseous ionization, and other details, such for example as the spacing of the electrodes and the voltage atwhich the tube is to be operated, are controlled by this factor.

It is an object of our invention-to provide 7 an X-ray tube having a greatly simplified construction with respect to prior art tubes.

Another object is the provision of an X-ray tube so constructed that the relation of the electrodes thereof, and the form of mounting therefor, obviates the necessity of having a vacuum as high as that required in other forms of tubes having similar characteristics, i. e., using the same range of operating voltages, etc.

Another object of our invention is'to pro vide an X-ray tube adapted to operate at a relatively high voltage and with a relatively high vacuum therein, but so. designed that the vacuum need not be as high as normally required in a pure electron-flow X-ray tube, because of the close spacing of the active faces of the electrodes and the restricted areas around other portions of said electrodes.

Another object of our invention is the provision of an X-ray tube in which the electrodes thereof are so assembled prior to introduction thereof into a bulb, as to comprise a unitary mount, which ma be sealed into the bulb after assembly in the'same fashion as a lamp mount is sealed into an incandescentelectric lamp.

Another object is provi-ding an electrode the degree of vacuum depending upon assembly which may be supported from one stem of the tube.

A further object of our invention is the prov1s1on of an X-ray tube having a single stem supporting theanode and an insulating attachment on said anode for supporting the cathode and properly spacing and insu latmg it from the an de.

A further object of our invention is the prov1s1on of an X-ray tube in which the anode or target is almost entirely enclosed by an msulatmg member which serves the double purpose of a support for the cathode and means for absorbing stray X-ra'diation, said msulatmg member bein provided with a focusmg device positioned opposite the working face of the anode for focusing electrons from the cathode thereon.

A still, further object of our invention is the provision of an X-ray tube in which both cathode and target are supported from a single stem and closely spaced and insulated from each other by means of a refractory in-- sulating member, with a metal absorption screen on the outslde of said insulating member for absorbing stray X-radiations and provided with a central aperture for allowing a useful cone of X-rays to emerge therefrom.

An additlonal object of our invention is the provision of an X-ray tube, of improved construction in which an incandescent electron-emitting cathode is provided generat-,

ing an electron stream which flows to the anode or target substantially along the\longitudinal axis of the tube and of the target, im-

pinges on the working face of the target and generates a main beam of 'X;rays which flows back along the same axis through the center of said incandescent cathode and out of the tube.

Other objects and advantages of the invention will become apparent as the description proceeds.

According to thepresent invention, a preferred embodiment of our novel form of X-ray tube comprises an evacuated'bulb or envelope formed with a main substantially spherical or spheroidal portion and an auxiliarysubstantially cylindrical extension therefrom. This extension preferably holds the target or anode of the tube and is provided with a screw-plug, electrically connectcd to said target, so that the tube may be conveniently connected, disconnected or replaced, for convenient use with auxiliary iqiparatus, such as a high-voltage trans former, delivering current at from 40,000 to 60,0100 volts, with which it is adapted to be user The cathode, which is formed as one or more turns of refractory wire or filament, is supported by and spaced from the anode by means of an insulating refractor member which substantially surrounds t e anode. As a means for energizing the cathode, leading-in conductors are provided, extending into the tube, preferably through the main portion thereof, substantially opposite to the cylindrical extension in which the anode is su orted.

lie anode or target is preferably formed of copper or other non-refractory metal with an insert of thorium or other refractory metal of high atomic weight, for example, uranium, serving as the focal surface for efficiently generating X-rays. The cathode which is supported close to said thorium insert, is preferably formed of tantalum or other refractory metal, such as as tungsten, molybdenum or may be oxide-coated platinum. Inside of the insulating member andadapted to support and space the cathode is a substantially cylindrical focusing device surrounding the cathode.

The focusing device may be provided with r a cup-shaped extension toward the target and is preferably formed ofinsulating material like that forming the support and insulation between the anode and cathode. If the supporting and insulating member is formed of material, such as lavarock, the same may either be made thick enough adjacent the focal surface of the target to absorb substantially all misdirected X-radiation or-a metallic absorption screen in the form of a cup, closely fitting the exterior of the insulating support, may be provided. The insulatmg support, focusing device and absorption screen, if used, are centrallytperforated so that a useful cone of X-rays may pass therethrough, along the common axis of the tube and anode. The insulating support is preferably formed nearly as large, in diameter, as the cylindrical extension of the bulb so that the space therebetween is restricted to minimize ionization.

All parts of the aforementioned electrode assembly, that is the anode or target, the surrounding insulating member, the focusing device and the ineandescible cathode supported thereby are assembled and formed into a mount, that is, secured to a stem in any desired manner prior to sealing into the bulb. Such a mount may then be sealed into the bulb in the same manner as a lamp mount is inserted into its bulb.

Our invention will be better understood by referring to the accompanying drawing, in which;

Fig. 1 illustrates a preferred form of our tgi-ray tube, shown partly in longitudinal secion;

Fig. 2 shows, in section, a modified form of stem for our tube.

Fig. 3 illustrates still another form of stem for the tube.

Fig. 4 is a drop perspective showing the elements of the electrode assembly;

Fig. 5 is a plan of our focusing and cathodepositioning device with the cathode shown in position; and,

Fig. 6 is a side elevation of the device shown in Fig. 5.

The envelope or bulb 1 of our tube is preferably constructed with a main substantially spherical or spheroidal portion 2 of relatively large radii of curvature and an auxiliary, substantially cylindrical extension 3. This cylindrical extension is preferably provided with a screw-plug 4, adapted to be inserted in a receptacle or socket of a type similar to those in which ordinary large incandescent lamps-are operated. Such a receptacle may form part of a casing of an enclosed transformer or any other auxiliary apparatus desired, used in connection with our X-ray tube. Although the main portion 2 of the tube is shown substantially spherical, it may be made substantially cylindrical, like its extension 3, and merely largeenough in diameter to avoid undue heating thereof. If cylindrical, its axis should correspond substantially with that of the extension 3 and contained electrodes.

It will be noted that the X-ray tube of the present application is substantially symmetrical about its longitudinal axis. A single stem 5 which supports both electrodes and other interior members in the tube, is provided. On accountof this construction, the entire interior structure of the tube may be assem bled in proper relation before insertion and sealing into the bulb.. I

Supported from the stem 5, preferably by means of a split cylindrical, resilient metal sleeve 6, is an anode or target 7, which may be connected to the member 6 in any desirable manner, as by being threaded into a plug 8 thereof, as shown. The plug 8 may be connected to the sleeve 6 in any desired manner,

'- as by pins 9.

nesium silicate, turned to the desired sha )e and then baked, may be held in position y fitting it over a.reduced section 12 of the anode 7, which section is'provided with a threaded portion which is then screwed into the end of the member 6, or plug 8 thereof, to thereby rigidly hold both the anode 7 and insulating member 11 in position by engagement of the shouldered portion formed onthe target, with the cooperating reduced annu .lar 1')ortion of the member 11 which closely fits the" reduced portion 12.

Inserted into the free end of the insulating member 11 is a substantially cylindrical focusing device 13, preferably comprising lava rock turned to shape and baked, in the same manner as the supporting member 11.' The focusing device 13 is preferably provided with a cup-shaped extension toward the target 7 as shown, which may partially enclose the focal area of the target and absorb stray X-rays therefrom. This extension'is adapted to snugly fit the end of the lavarock support. The interior of the cup is preferably substantially hemi-spherical. A cylindrical flanged extension 14 is preferably provided on the focusing device. I A filamentary cathode 15, preferably formed as a coil of tantalum wire, is supported close to the focal insert'lO,

by means of the focusing device, as more fully described in connection with Figs. 5 and 6. It is clear,'h0wever, that the cathode may be formed of. platinum or the like coated with alkaline earth material, or formed of other refractory metal besides tantalum.

Unless the lavarock insulating member 11 and focusing device 13 are made relatively thick, so that stray X-radiation is absorbed thereby, a metal absorption screen 16, preferably formed as a nickel cap, is provided enclosing the end of the insulating support 11, adjacent the focal insert 10 of the target 7. This absorption screen 16 may support the focusing device 13 and be connected to the insulating support 11 in any desiredmanner.

The cathode 15 may be energized by means of leading-in conductors 17 and 18 extending through the bulbous portion of the tube at 19 and 20, substantially opposite to the cylindrical extension?) and screw-base 4 thereon. The cathode, if of tantalum or other metal having a correspondingly high melting point, may beOperatedat such a degree of incan d'escence that no anode material will distill thereto and condense thereon. This willavoid activation of the cathode by distilled thorium from the anode, if thorium for example, is so used, with a consequent increase in emissivity and current through the tube. In this way more uniform operatin characteristics are obtained. The target is provided with a leading-in conductor 21, connected thereto in any desired manner, for example, by means of screw 22. The other end of the conductor 21 is electrically connected to the center'cont-act of the screw-base 4, by means of solder, for example, for introducing the desired current thereto; q 1

In constructing our present form of tube, the insulating support 11 and focusing device 13 are preferably formed of lavarock, lavite or soapstone, by turning the same on a lathe, although, as is obvious, other insulating materials such as porcelain, fused quartz, thoria or the like may be used. After turning to shape, these insulating members, if of lavarock, are baked at about 1100 C. This treatment hardens them, eliminates moisture and increases the insulating properties thereof.

The baking operation of the lavarock should be conducted in the air or other oxidizing atmosphere and ordinarily a change in color is eflected during the'baking operation. After thelavarock members are put into service in the tube or during the treating of the electrodes preparatory to sealing off the tube, care must be taken not to over-heat the lavarock members in the vacuum, because if this is done, a loss in insulating properties is effected. That is, it may be that some re ducing gas, such as hydrogen, is left when the bulb is exhausted, or developed during the operation of the tube, so that if the lavarock members become heated beyond a certain point, a change in color takes place with an increase in their conductivity, so that their insulating qualities are seriously impaired.

After the electrodes and elements as'sociated therewith are assembled in proper relation outside of the bulb, they are applied to the stem 5 and inserted bodily into the cylindrical extension 3 thereof and the stem 5 sealed therein to hold them in place. The leading-in conductors 17 and 18, to the filamentary cathode 15 may be threaded through apertures provided at 19 and 20 when the electrode assembly is inserted into the bulb, after which these apertures are sealed, as shown at 19 and 20,

The bulb is exhausted and the electrodes treated in any. desired manner to free them from gases and vapors. The tube may then be operated with the filament 15 at incandescence and one of the leading-in conductors therefor grounded, so that the only portion of the tube at high-potential is the anode end or screw-base 4. The desired high-potential is axis of the anode, through the aperture 23 of' the focusing device 13 and metal absorption screen 16, if used, as a useful cone of X-rays. By means of this construction, va good focus is obtained on the focal surface of the vice 13 will have acquired'a negative potential from electrons impinging thereon and serves to focus the electron stream in a manner as efliciently as if it were a metal focusing device electrically connected to the cathode. Pin-hole photographic picturesof the target taken by means of X-rays during 1 operation of the tube, show very good focusing, in fact as good as that obtained when conducting focusing means are used. When using the absorption screen 16 of nickel or the like, it is found that the lavarock may be made relatively thin and yet substantially all stray X-radiation is efficiently absorbed by the screen.

Three stem constructions and two scalingin arrangements are illustrated in the drawing and the constructional details thereof are as follows. In Fig. 1 the stem 5 supporting the electrode assembly is open at its inner end and requires two sealing-in operations for completion. That is, before sealing-in, the cylindricalextension 3 ofthe bulb 1 extends beyond the point'at which the stem 5 is connected thereto and is of uniform diameter. lVhen assembling the various parts, the leading-in conductor 21'is sealed through the tube 24 at the press'25. This tube 24 is preferably provided with a slight outward j flare at its outer end'26.

The stem 5 with the electrode assembly thereon, is held in a suitable manner, preferably by means of a split hollow holder,,insorted in the extension 3 and the flare 27 of stem 5 sealed thereto at 28. The leading-in conductors 17 and 18, atthe time of insertion, are preferablyv threaded through apertures or tubulature at 19 and 20. That portion of the extension 3 beyond the seal 28 is then heated and drawn to form the tapered portion 29, the outer end of which is sealed to the tube 24 at the flared portion 26. All this may be accomplished before exhausting and before the leading-in conductors 17 and 18 are scaled through the glass at 19 and 20.

One of these conductors, 17 for example, may then be sealed through the glass and a portion of the tapered part 29 heated while pressure is applied at the aperture fon the leading-in conductor 18 to blow a hole at 31 for purposes of exhaust. A -suitable exhaust tube is then connected'at 31, leading-in conductor 18 for the cathodesealed at 20 and the tube exhausted and tipped off in the usual manner. After this has been accomplished, the screw-base 4, which may be the usual form of mogul base, is applied thereover as shown, the leading-in conductor 21 extending through the central electrode 32 to at 33 as s own.

Although this leading-in conductor is shown connected to the central electrode 32, it is obvious that, if desired, it may be connected to the outer or threaded electrode 34. The space between the screwbase and the tapered portion 29 of the tube is filled with a suitable cement 35, before the base is applied to the bulb.

The ends of the leading-in conductors 17 and 18 are brought through and sealed into the bulb forming protuberances 19 and 20, which are subsequently crowned with conthereof and referably being soldered theretact caps 36 and 37 cemented thereon and provided with central apertures through which the leading-in conductors 17 and 18 are threaded and soldered thereto.

The modified construction illustrated in Fig. 2 avoids the necessit of a seal corresponding to that between t e tapered portion 29 and tube 24. In this modification a stem 43, of a type similar to that used on lamps of the tipless.variety, is preferably employed, That is, the stem 43 has the leadingin conductor 21 sealed therethrough at 44 so that it is closed, rather than open, at its inner end. It is however, provided with an exhause tube 45 preferably extending from,

near the inner end thereof, to beyond the other end of the stem.

Inorder to seal-off a tube with this type of construction, it is merely necessary to form the single seal at 46 between the flare 47 on thestem 43 and the extension 3 of the tube. This makesit possible to make the electrode assembly complete, connect it in place on the stem and seal the stem in one operation into the bulb at 46, after which it is, merely necessary to exhaust'the bulb through the exhaust tube 45 and tip-oft at 48. Of course, it is also necessary to seal the leadlng-in conductors 17 and 18 of the cathode 7 through the glass, the same as for the first modification as illustrated in Fig. 1.

As in Fig. 1, the screw-base 4 of Fig. 2,

is applied in the same manner, but it will be noted that it fits down over the main portion of the extension 3 to a greater extent than nal slot 49 and a transverseislot 50 joining therewith, so that the free Wings of the sleeve formed, serve to resiliently hold the assembly in position on the stem. Although the cathode assembly may be merely frictionally I held in position, it is preferable to lock the same securely on the stem. For that purpose, a bayonet slot or slots 51 may be prov ded 1n, the sleeve and a lug or In s 52 sealed onto the stem 5 or 43 or both. T e cathode assembly may be securely locked in place by inserting the split sleeve over the stem with the bayonet slot 51 engagingthe lug 52 until the inner transverse portion of the slot is reached, after which the sleeve is twistedon the stem to the position shown in Fig. 2, when the sleeve is securely locked in position, as will be understood.

Fig. 3 shows a modified form of stem 43' for the tube, which is like the stem 43 shown in Fig. 2, except that the exhaust tube 45' joins directly with the press 53, through which the leading-in conductor 21 extends, instead of being sealed into the stem independently of the press. Such a stem is adapted for manufacture on a machine for making stems for the usual type of tipless incandescent electric lamps. The press is formed with the aid of air pressure, applied to the exhaust tube 45' to blow a hole through the press into the bulb, so the press 53 contains a bulbular device 13 cavity 53 between the exhaust tube 45 and.

the hole to the interior of the bulb.

Fig. 4 is a drop perspective to. illustrate the order of assembly of the various electrode elements. From this it will be clear that the anode 7 is inserted into the insulator 11 and screwed into the plu 8 of, the split sleeve 6 which is attached to t e stem 5. The focusing device 13 with the incandescible cathode 15 in place therein, is then inserted in the insulator 11 and the nickel cap 16 is then inserted thereover and held in place by screws on the like.

Figs. 5 and 6 illustrate, in detail, the insulating focusing device 13 and tlige incandescible cathode 15 in position therein. As clearly shown in these figures, the focusing referably comprises three main portions; 1) a central cylindrical portion 54; (2) an end cup-shaped portion 55 and (3) a flanged portion 14 at theopposite end.

The flanged portion 14 is provided with apertures 56, 58, through which the leads 17 and 18 extend in a direction parallel with the axis of the tube, after which they are bent at right angles and extend inwardly toward the axis to connect with the centrally-held incandesciblecathode'15. To provide for the insertion of said cathode 15 and for holding it securely in position, the focusing device is slotted at 57, as shown, in Fig. 5, said slot preferably extending through the cup-shaped portion 55 and part of the cylindrical portion 54. The'slot is preferably deeper at one side than the other, as shown, so that the coiled filament is supported properly when in the bottom of'the slot, the difference in depth corresponding to the pitch'ofthe coil. The incandescible cathode 15 and its connected leading in conductors may then be positioned in said slot with the free ends conductors extending through apertures 56 and 58. As supplemental means for spacing and positioning the incandescible cathode 15 the inner end of the insulator 11 is provided with slots 59 and 60 engaging the leading-in.

conductor elbows 61 and 62.

By means of the foregoing arrangement, the mcandescible filament is accurately positioned with respect to the cooperating focal portion 10 of the target, motion being prevented in one direction, after assembly, by the slots 59 and 60 and in the other direction by the inner end' ofthe slot 57. After the focusing device is positioned with its cathode 1n place, the shield 16, if used, is inserted thereo'ver and held in place in any desired manner, for example, by means of screws 63 and 64 exte'nding'through the shield 16, the insulating member 11 and into the focusing of the leading-in device 13 tohold them. rigidly together in 1 position. Apertures 65 and 66, larger than the apertures 56 and 58 in the focusing device, are preferably provided in the shield, so that short circuitingbetwcen the leading-in conductors-17 and 18 is obviated. Upon' again referring to Fig. 1, it will be noted that in accordance with the foregoing description, the insulating and supporting member 11 is formed of such a size that it iits the cylindrical extension 3 of the bulb fairly close. That is, the area 67, between the glass of the bulb and the insulating member 11, is quite restricted. The distance between the cathode 15 and the focal insert 10 of the target 7 is likewise relatively small. That is, it preferably ranges between 8 and 15 millimeters. An advantage secured by such a construction, is that the vacuum in the bulb 1 need not be as highas ordinarily required in an ordinary type of X-ray tube adapted to operate on a voltage, corresponding to that for which the present tube is designed, and still avoid a substantial amount of gaseous ionization. The vacuum, however, should be high enough so that the mean free path of electrons in the bulb is great compared to the distance between the active faces of the elec- I trodes, to avoid substantial Jgaseous ionization .therebetween, as will be understood.

Gaseous ionization between the cathode 15 and the outer portion of the target 7 and supporting sleeve 6 is mii'iimized and substantially eliminated by the restricted portion 67 between the bulb 1 and the insulating member 11 and the restricted area between the target 7 and the insulatingmember 11, it being apparent from the drawing that the insulating member 11 is designed to closely surround the target 7 v As an example of what a tube of the foregoing construction will accomplish, it may be stated that in operating such 'a-tube on alternating current of 50,000 volts maximum with 5 milliamperes of current therethrough,

vantage is secured with a tube according to the present construction where the patients may be positioned very close, because of the absence of danger from shock at the cathode and of the tube. One of the leads to the cathode may be grounded so that the other is at a potential merely high enough to cause the heating current therefor to flow through it. For this reason, the'patient may get as close as is necessary to the cathode end of the tube, in the path of the useful cone of X-rays emerging from the aperture in the focusing device and X-ray screen, it used.

As previously mentioned, very good focusing is secured with a tube of this type so that good definition is attained even when the object radiographed is positioned very close to the tube. Because of the absence of hightension leads. in that part of the tube adjacent the object radiographed, very close positioning is permissible without danger. In-

, asmuch as the length of exposure ma be very much shortened by close spacing 0 the object with respect to the tube, in accordance with the law aforementioned, it will be seen that a tube of the present construction has a great advantage over thev usual typeof X-ray tube where close positioning is impossible. If it is desired to run the tube on Varying voltages and currents so that care must be taken to avoid overheating the target and particularly the copper or non-refractory portion thereof, it is preferable to have one or more apertures 68 in the insulating member 11, so that the degree of heating of the target 7 may be observed, while in operation. As an alternative or auxiliary, an instrument for registering the degree of heating of the tar et, may be used. filthough a preferred embodiment of our invention is illustrated, it is obvious that modifications may be made therein, without departing from the spirit and scope of the What is claimed is:

1. An X-ray device comprising an evacuated envelope provided with a target and a stem supporting the target, an insulating member surrounding said target and an ininvention, as defined by the appended claims.

candescible filament supported by said in- Sula-ting member.

.2. An X-ray device comprising an evacuated envelope enclosing an anode and acathode, a focusing device surrounding the cathcathode in support extending ode and an insulating df d mg sal OCuSlIlg 5. In an X-ray tube, an anode and an electron-emitting cathode supported from the anode and spaced with respect thereto, by means of an insulating member.

6. An X-ray device comprising a plurality of electrodes supported from a single stem, and an auxiliary-tube in the stem for exhausting the device.

7. An X-ray device comprising an enclosing envelope including a stem portion, an anode or target mounted thereon, aninsulating and spacing member supported on said target and an incandescible cathode sup ported by means of said insulating member and spaced in given relation to the target.

8. An X-ray device comprising an evacuated envelope enclosing an anode and a cooperating electron-emitting cathode, a non.- conducting focusing device surrounding the cathode and provided with an aperture for allowing X-rays generated on the target to pass out of the tube along the axis of the electron stream.

9. In a high-voltage electrical device, an anode, an electron-emitting cathode and an insulating focusing device surrounding the cathode.

10. An electrode assembly for an X-ray device comprising a split sleeve formed of resilient material and adapted for application to the stem of an enclosing envelope, a refractory insulating and spacing member, an anode member threaded to the split sleeve and extending through a portion of the insulating member and provided with a shoulder engaging said insulating member, whereby when the anode'is threaded into the sleeve it rigidly maintains said three members in alignment and in given spaced relation, and means in the opposite end of the insulating member for supporting an incandescible proper relation with respect to the target. I

11. An electrode assembly for an X-ray device'comprising a resilient sleeve adapted for engagement with a substantially cylindrical stem of an enclosing envelope, said sleeve being provided with a threaded plug incandescible cathode maintained in position by said device. v

y 12. An electrode assembly for an X-ray device comprising a resilient sleeve adapted for engagement with a substantially cyhndrical stem of an enclosing envelope, said sleeve being provided with a threaded plug portion in one end thereof,an anode provided with a threaded extension engaging said plug portion and a substantially cylindrical insulating member through which a portionof the anode extends and which is held to said sleeve member by the engagement of a shouldered portion ofthe anode therewith, when the same is threaded into the plug portion of the sleeve, said insulat ng member supporting an insulating focusing device at its opposite end, an incandescible cathode maintainedin position by said device and a shield member extending over the focusing device attached to the end ofthe insulating member and provided with a central aperture whereby a useful cone of X-rays is permitted to pass therethrough and stray X-radiation absorbed.

13. An electrode assembly for an X-ra device comprising a stem, a split resilient s eeve engaging said stem, an anode and surrounding insulating member rigidly connected to said split sleeve by means of a threaded engagement and a cooperating incandescible cathode accurately positioned with respect to said anode whereby the whole assembly may be completed before the same is introduced and sealed into an enclosing envelope.

14. An electrode assembly for an X-ray device comprising an anode, a cooperating incandescible cathode and -supporting means therefor between said anode and cathode, means for supporting said assembled electrodes comprising a split resilient 'sleeve adapted for application toa stem of, an en-' closin envelope and means for locking said assem ly in position on the stem comprising a lug on the stem and a bayonet slot on the sleeve adapted for interlocking engagement with said lug.

15. An electrode assembly for an X-ray device comprising an anode or target, an lnsulatingmember of lavarock rigidly connectedthereto and substantially surrounding the same, and a cathode supported by means of said insulating member.

16. In an 'X-ray device, an enclosing envelope rovid'ed w1th a stem, a sleeve supy said sleeve and holding in place a substan-' tially cylindrical insulating member, said insulating member surrounding said target, bolted to the sleeve by the threaded engagement of the target therewith and havin attached theretoa focusing device with a slotted portion, and an incandescible cathode-held in the slotted portion whereby the cathode is spaced and accurately positioned with respect to the anode or target, for the production of 'X-rays thereon.

'17.'In an X-ray'device, an enclosin envelope provided with a stem, a split s eeve supported thereon by resilient frictional engagement, an anode or target supported by. means of threaded engagement with' said sleeve and holdin in place a substantially cylindrical insulating member, said insulating member surrounding said target, bolted to the split sleeve by the threaded engagement of the target therewith and having attached thereto a focusing device with a slotted portion, and an incandescible cathode held in the slotted portion whereby the cathode is spaced and accurately positioned with respect tothe anode or target, for the production of X-rays thereon. p

' 18. In an X-ray device, a target comprising a body of non-refractory metal into which is threaded and pressed a focal insert of a refractorymetal of high atomic weight.

19. In an X-ray device, a target comprising a body of copper into which is threaded and pressed a focal insert of thorium.

20. In an X-ray tube, an X-ray shield surrounding the cathode and focal portion of ghehtarget and electrically independent of 21. In an X-ray tube, a single electrode supporting stem, a metal X-ray shield surrounding the cathode and focal portion of the target and supported from said stem.

22. An X-ray device comprising an evacuated bulb with a substantially cylindrical extension therefrom an anode supported in said extension and c osely surrounded by an insulator supporting a cooperating incandescible cathode in close relation to the'anode,

only, that the mean free path of electrons is great compared to the spacing of the electrodes, said insulating member being large ported t ereby, an anode or target supported .the bulb being evacuated to such a degree enough to restrict the area between it and the surrounding extension of the bulb, so that gaseous ionization is substantially absent when the tube is in operation.

23. The method of making an X-ray device comprising connecting an anode toa stem while supporting aninsulating element onthe stem by means of said anode and supporting an incandescible cathode in properrelation with respect to said anodeby means of said insulating element, all of said operations cathode from said insulating means and sealbeing performed prior to inserting into a ingsaid stem and supported members into 10 bulb. a bulb.

24. The method of making an X-ray de- I In testimony whereof, we have hereunto 5 vice comprising supporting a target on a subscribed our names this 18th day of Octostem, supporting an insuiatin member byv ber,1924, v means of said target, supporting a holding CLAYTON TRIDLE ULREY. means for an incandescible filamentary V HARRY DIE "FOREST MADDEN. 

